In general, a gas turbine needs several fluids for start-up and maintenance. First of all, a combustible gas or a liquid fuel may be injected into a combustion chamber, wherein it is mixed with compressed air and burned. A water injection also may be required to reduce nitrogen oxides (NOx) and the like generated during operation of the gas turbine. In addition, the water injection may be used to purge in order to evacuate residual combustible fluids in the circuits of the gas turbine, for instance after changing liquid fuel operation to gas fuel operation or when stopping the gas turbine. Air also may be injected into the combustion chamber for purging or for sweeping or cooling the nozzles when they are no longer feed with liquid fuel during gas fuel operation and the like. In order to regulate the selective passage of one or several of these fluids, it is necessary to position a multi-way valve upstream of the combustion chamber.
In addition, liquid fuel operation may increase generation of NOx emissions. Thus, a gas turbine may be provided with two separated injection circuits, a primary circuit and a secondary circuit, which may enable a reduction of NOx emissions by an injection of liquid fuel at partial load operation and at nominal load. The gas turbine can in that way operate according a first mode wherein only the primary circuit is fed with a combustible fluid. This mode may be used for start-up, acceleration, and part load operation for a limited preselected combustion temperature. According to a second operation mode, the primary and the secondary circuits may be feed at the same time. This mode may be used for partial load operation limited until full load, between the two preselected combustion temperatures or another combustion parameter such as the dynamic pressure in the combustion chamber. Thus, it may be necessary to manage the opening and closing of each circuit, in particular the inlet and outlet of each one, in order to provide these different operation modes of the combustion chamber in the gas turbine.
Using the liquid fuel may require the water purge and the air sweeping steps in the turbine circuits, as mentioned above. In addition, the stagnant liquid fuel tends to solidify in the presence of air and hot temperatures in a process known as cokefaction. As such, it is important to execute these steps before and after any change between liquid or gas fuels and during gas turbine shutdown. In order to reduce the volume of residual liquid fuel it is necessary to place a distribution valve as closer as possible to the combustion chamber so as to avoid a sudden increase in the power output due to a volume of fuel sent to the combustion chamber during the purge, also known as power output step.
Up until now, several types of multi-way valves have been developed. U.S. Pat. No. 6,289,668 describes in particular a solution based on a rotating mechanism that enables a selective feeding of a liquid combustible and/or water in a combustion chamber. The multi-way valve disclosed includes two concentric cylinders with an inner cylinder mounted for rotation inside an outer cylinder. Depending on the position of the inner cylinder about the rotational axis, the surface of the inner cylinder blocks circuit openings into the outer cylinder or unblocks these openings through slots provided in the surface. This arrangement of elements enables a selective flow of several fluids by rotation of the inner cylinder. This mechanism, however, may cause metal friction between the two cylinders that may result in a significant torque to be applied and a quick wearing of the cylinders such that a risk of leaks between the ports may be increased.
U.S. Pat. No. 3,098,506 also discloses a multi-way valve that includes a housing and a movable actuator. Means for tightness, which includes two deformable sleeves made of a polytetrafluoroethyle (PTFE) polymer, may be placed between the housing and the movable actuator. The material of the sleeves prevents friction therebetween. An effective seal may be maintained between the movable actuator and the housing by a pair of deformable sleeves that serve both as effective bearings for the actuator and as an effective seal between the actuator and the housing. These deformable sleeves may be separated by a relatively rigid intermediate member. The effectiveness of the seal afforded by the deformable sleeves may be controlled by means which apply axial forces against the outer edges of the deformable sleeves so as to compress each of the deformable sleeves against the intermediate rigid member while still serving as effective bearings for the common actuator arrangement. However, this arrangement also may provide a significant torque to the movable actuator to overcome the friction between the housing and the movable actuator. In addition, this arrangement also may require manual operation to maintain a continuous seal.
Thus, one of the aims of the application herein is to overcome these drawbacks by providing a multi-way valve having a reliable mechanism that is easy to manufacture and avoids an increase in the torque supplied to the actuator over time.